Changes in motor vehicle internal combustion engines to improve fuel economy and/or to reduce carbon emissions have led to “undersized engines”—the utilization of smaller engines in vehicles that are larger than those smaller engines were originally intended to serve. Efforts to reduce friction, to reduce pumping work and to address other challenges have yielded engines having fewer combustion cylinders and/or smaller displacements than predecessor engines. At low load, the throttle of a traditional engine is substantially closed, reducing engine cylinder pressure. In such a situation the engine has to work to draw combustion air into the cylinders, thus causing a pumping loss that reduces engine efficiency and lowers fuel economy. Friction reduction has been achieved by reducing the number of combustion cylinders in engines and/or reducing the engine's displacement, again resulting in reduced engine power.
Turbochargers have been employed to improve engine torque, but have introduced a performance problem for drivers; turbocharged engines have suffered from turbo lag during acceleration. These new configurations thus naturally result in both lower power and poorer performance at tip-in and slow speeds. In addition to the negative impacts on performance, fewer cylinders and/or smaller displacements mean reduced engine power more generally. New ways have been sought to generate additional power to compensate for these deficiencies. Some solutions have utilized twin-scroll, dual-nozzle and variable-geometry turbochargers, which add complexity to an engine's operation and layout.
Some earlier engine systems have replaced conventional throttle butterfly valves with intake-valve-controlled throttling that uses an electrical, electromechanical and/or hydraulic mechanism to control individual intake valve lift for each cylinder to regulate combustion air flow into the cylinder. These systems use a stepper motor to control a secondary eccentric shaft fitted with a series of intermediate rocker arms, which in turn control the degree of valve lift. The throttle butterfly valve is no longer used to control the cylinder's combustion air supply, though for safety reasons it is still fitted as an emergency back-up. Thus these earlier systems have additional hardware the increases the complexity of crankshaft operation. Moreover, because the intake valves are used as combustion air control valves, tremendous spring and frictional valve spring forces and operational characteristics must be addressed and overcome with an intake valve throttling operation. These heavy spring and frictional forces diminish the responsiveness of these intake-valve-as-throttle systems.